Recharge system and method for deep or angled devices

ABSTRACT

Techniques are disclosed for recharging an Implantable Medical Device (IMD). In one embodiment, a first external coil is positioned on one side of a patient&#39;s body, such as on a front side of the torso in proximity to the IMD. A second external coil is positioned on an opposite side of the patient&#39;s body, such as on the back of the torso. A recharging device generates a current in each of the coils, inductively coupling the first and the second coils to the secondary recharge coil of the IMD. According to another aspect, each of the two external coils may wrap around a portion of the patient&#39;s body, such as the torso or head, and are positioned such that the IMD lies between the coils. According to this aspect, current generated in the coils inductively couples to a second recharge coil that is angled within the patient&#39;s body.

RELATED APPLICATIONS

This application is a continuation of, and claims priority to, U.S.patent application Ser. No. 12/108,051 filed Apr. 23, 2008, now allowed,which is incorporated herein by reference in its entirety.

FIELD OF THE INVENTION

This invention relates to IMDs and, in particular, to energy transferdevices, systems and methods for IMDs.

BACKGROUND OF THE INVENTION

Implantable Medical Devices (IMDs) for producing a therapeutic result ina patient are well known. Examples of such IMDs include, but are notlimited to, implantable drug infusion pumps, implantableneurostimulators, implantable cardioverters, implantable cardiacpacemakers, implantable defibrillators and cochlear implants. Such IMDsmay treat a variety of symptoms or conditions including, but not limitedto, chronic pain, migraine headaches, tremor, Parkinson's disease,epilepsy, incontinence, gastroparesis, heart failure, tachycardia, andbradycardia.

A common element in all of these IMDs is the need for electrical powerin the device. The IMD requires electrical power to perform itstherapeutic function, which may include driving an electrical infusionpump, providing an electrical neurostimulation pulse and/or providing anelectrical cardiac stimulation pulse, for example.

Typically, a power source for an IMD can take one of two forms. Thefirst form utilizes an external power source that transcutaneouslydelivers energy via wires or radio frequency energy. Having electricalwires which perforate the skin is disadvantageous due, in part, to therisk of infection. Further, continuously coupling patients to anexternal power source for therapy is a large inconvenience.

A second type of power source utilizes single cell batteries as theenergy source of the IMD. This can be effective for low-powerapplications, such as pacing devices. However, such single cellbatteries usually do not supply the lasting power required to performnew therapies in newer IMDs. In some cases, such as an implantableartificial heart, a single cell battery might last the patient only afew hours. In other, less extreme cases, a single cell unit might expelall, or nearly all, of its energy in less than a year. This is notdesirable due to the need to explant and re-implant the IMD or a portionof the device.

One way to address the aforementioned limitations involvestranscutaneously transferring electrical power through the use ofinductive coupling. Such electrical power may then be optionally storedin a rechargeable battery. In this form, an internal power source, suchas a battery, can be used for direct electrical power to the IMD. Whenthe battery has expended, or nearly expended, its capacity, the batterymay be recharged. This is accomplished transcutaneously usingelectromagnetic coupling from an external power source that istemporarily positioned on the surface of the skin. Most often this willinvolve inductive coupling, but could include other types ofelectromagnetic coupling such as RF coupling.

Transcutaneous energy transfer through the use of electromagneticcoupling generally involves the placement of two coils positioned inclose proximity to each other on opposite sides of the cutaneousboundary. An internal, or “secondary”, coil is part of, or otherwiseelectrically associated with, the IMD. An external, or “primary”, coilis associated with the external power source, or recharging device. Therecharging device drives the primary coil with an alternating current.This induces a current in the secondary coil through inductive coupling.This current can then be used to power the IMD and/or to charge, orrecharge, an internal power source.

For IMDs, the efficiency at which energy is transcutaneously transferredis crucial for several reasons. First, the inductive coupling has atendency to heat surrounding components and tissue. The amount ofheating of surrounding tissue, if excessive, can be deleterious. Byincreasing the efficiency of the energy transfer between the primary andsecondary coils, heating of the tissue is minimized. Moreover, the timerequired to complete the recharge session is minimized, therebymaximizing patient convenience. Finally, if more energy may betransferred in a shorter period of time, IMDs may be employed that havehigher power requirements and that provide greater therapeutic advantageto the patient.

One way to increase energy efficiency is to position the primary coiloptimally with respect to the secondary coil. This generally involvespositioning the primary coil on the patient's body (e.g., on their skin)as close to the secondary coil as possible. Moreover, the primary coiloptimally lies in a plane that is parallel to the plane occupied by thesecondary coil within the patient's body. This configuration is readilyachieved in an implant scenario wherein the coil is implanted at a depthof between 1 and 3 centimeters in an orientation such that the IMD ispositioned roughly parallel to the cutaneous boundary. This type ofscenario may be used when an IMD is positioned within the pectoralregion, as will be the case if the device is to be used to deliverelectrical stimulation to areas of the brain, for instance.

In some cases, an IMD may be implanted more deeply within a patient'sbody. For instance, when an IMD is used to deliver therapy related tosacral nerve stimulation (SNS) as may be performed to treatincontinence, the IMD may be implanted more deeply within the abdominalcavity. When so implanted, the IMD may not be parallel to any particularcutaneous boundary, and in fact, may actually be perpendicular to suchboundaries. As a result, less efficient recharge coupling is achieved,requiring longer recharge sessions.

SUMMARY OF THE INVENTION

In general, the invention is directed to techniques for recharging anIMD that is implanted more deeply within a patient's body (e.g., morethan 3 cm) and/or that is angled within the body such that a secondaryrecharge coil of the IMD is not parallel to an adjacent body surface. Inone embodiment, the invention relates to positioning a first external,or primary, coil (“first coil”) on one side of a patient's body, such ason a front side of the torso proximal to the IMD. A second external coil(“second coil”) is positioned on an opposite side of the patient'storso, such as on the back of the patient proximal to the IMD. Arecharging device generates a current in each of the coils,electromagnetically coupling the first and the second coils to thesecondary recharge coil of the IMD. The use of the two coils increasesthe electromagnetic coupling that is achieved for deep-implantscenarios, increasing efficiency with which a rechargeable power sourcemay be recharged.

The above example describes first and second coils positioned onopposite sides of the torso. The mechanism is of particular use for animplant located within the torso, since IMDs located within this regionmay most likely be more than 3 cm from a cutaneous boundary. However,the mechanisms described herein may likewise be applied to an IMDlocated anywhere within a patient's body, including head, neck, arm,leg, chest, pectoral region, hand, foot, and so on.

As discussed above, one variation of the invention arranges two coilssuch that a surface of each coil is substantially flat against a surfaceof the patient's body. For instance, a first coil may be substantiallyflat against a front of the patient's torso while a surface of thesecond coil is substantially flat against the back of the patient'storso. This configuration is particularly effective in recharging an IMDthat has a secondary recharge coil located in a plane that issubstantially parallel to the front and back surfaces of the patient'sbody. In other words, this configuration is most effective if the IMD isnot angled with respect to an adjacent surface of the patient's body.This is true because in this configuration, planes in which the firstand second coils lie are substantially parallel to the plane carryingthe secondary recharge coil of the IMD, which provides a scenario inwhich optimal coupling may be achieved between the first and secondcoils and the secondary recharge coil.

In another scenario, the IMD may be angled so that a plane carrying thesecondary recharge coil is not substantially parallel to adjacentsurfaces of the body. In a most extreme case, the secondary rechargecoil may be carried in a plane that is transverse to the adjacentsurfaces of the body. To address this type of scenario, an embodiment ofthe invention provides first and second coils that encircle, or arewrapped around, a portion of the body. The coils are positioned so thatthe IMD is located between the two coils. This provides a configurationin which planes carrying the first and second coils are substantiallyperpendicular to adjacent surfaces of the body and are substantiallyparallel to a plane carrying the secondary recharge coil. As discussedpreviously, this allows for better electromagnetic coupling between thefirst and second coils and the secondary recharge coil, therebyproviding more efficient recharge of the rechargeable power source.

The first and second coils may be coupled to the recharging device invarious ways within the scope of the invention. For instance, the firstand the second coils may be electrically coupled in series to therecharging device such that the recharging device generates a current inboth coils at once via a single port, or connection. Alternatively, eachof the first and second coils may be connected to the recharging devicevia different ports, with the recharging device generating current ineach of the coils independently. According to one aspect, each of thecoils carries a current having the same amplitude, frequency, and phase.

Another aspect of the invention aligns the first and second coilsaccording to a central major axis (“major axis”). As used herein, themajor axis of the coil is the axis that intersects the center of thecoil and is perpendicular to a plane in which the coil lies. The firstand second coils may be aligned so that they substantially share thesame major axis. According to another aspect, this major axis intersectsthe IMD, which lies between a first plane carrying the first coil and asecond plane carrying the second coil.

A support structure or support member may be provided to support atleast one of the first and second coils. This support structure may be atorso strap, a shoulder strap, or a holster. This support structure mayallow at least one of the first and second coils to be selectablypositioned. In one instance, the positioning is allowed to occur in twodimensions, such as vertically and horizontally relative to thepatient's body. For instance, a holster may be provided that includes afirst holder to receive or support the first coil and a second holder toreceive or support the second coil. The first holder may generally beadjacent to the front of the patient's torso, and the second holder maybe generally adjacent to the back of the patient's torso. Adjusters areprovided to allow at least one, and optimally both, of the positions ofthe first and second holders to be adjusted in at least one of avertical direction and a horizontal direction. In this manner, the firstand second coils may be aligned relative to each other. For instance,the first and second coils may be aligned to have a same major axis.

In one embodiment, the support structure may be other than a holster,shoulder strap, or torso strap. For instance, it may be a garment suchas a shirt, vest, shorts, sweat pants, or any other article of clothingthat carries or supports the coils. In each case, the coils arepositioned such that when the garment is donned, the coils are, in oneembodiment, located on opposite sides of the patient's body. In anotherembodiment, when the garment is donned the coils encircle, or wraparound, a portion of the patient's body.

In the alternative, a support member may include headwear, such as a hator a headset mechanism similar to that used to listen to a portableaudio device. The headwear may position the coils on opposite sides of apatient's head, or may instead support the coils so that they each wraparound the head. As yet another example, the support member may includea neck support that carries coils on either side of an inner surfaceadapted to receive a patient's neck. Arm bands, leg bands, and headbands could likewise carry the coils. These coils could be adapted toposition the coils on opposite sides of a portion of the patient's body,or instead to position the coils so they wrap around a portion of thepatient's body.

Another embodiment of the invention provides two structures that carryor support the first and second coils, respectively. For instance, thefirst structure, which carries the first coil, may be a mechanism onwhich the patient sits, such as a chair or chair pad. A secondstructure, which carries the second coil, may be a torso strap, agarment, or some other structure that supports the second coil in aposition that encircles the patient's body. The patient sits on thefirst structure while the second structure supports the second coil suchthat the IMD is located between the first and second coils.

According to another aspect, a first structure on which a patient liesis provided to carry the first coil. For example, this may include amattress pad. A second item such as a blanket or other mechanism meantto cover the patient is provided to carry the second coil. The coils maybe positioned on opposite sides of the body to recharge an IMD while thepatient is resting.

One embodiment of the invention relates to a recharging system for usein recharging an IMD implanted in a patient. The IMD has a secondaryrecharge coil and a rechargeable power source. This recharging systemincludes a first coil lying in a first plane and a second coil lying ina second plane substantially parallel to the first plane. The IMD liesbetween the first and second planes. A recharging device is coupled toeach of the first and the second coils to generate a current in thefirst and the second coils that electromagnetically couples the firstand the second coils to the secondary recharge coil to recharge therechargeable power source.

In the foregoing embodiment, the first coil is said to lie in a firstplane and the second coil is said to lie in the second plane. It shouldbe noted that this does not necessarily mean that all turns of amulti-turn coil lie within a same plane. For instance, multiple turns ofa first coil may be stacked one on top of another such that the turnsreside in different planes. In this case, the coil may be said to becarried, or lie within, multiple planes. Each of these multiple planeswill be substantially parallel to one another, and substantiallyperpendicular to a major axis of the coil. Thus, a first plane carryinga first coil may be any one of multiple planes in which the first coillies. Likewise, a second plane carrying the second coil may be one ofmultiple planes in which the second coil lies.

Another aspect of the invention relates to a recharging system for usein recharging an IMD implanted in a patient. The IMD has a secondaryrecharge coil and a rechargeable power source. The recharging systemcomprises first and second coils external to the patient's body andpositioned so that the IMD lies between the first and second coils witha major axis of at least one of the first and second coils intersectingthe IMD. A recharging device is coupled to generate a current thatelectromagnetically couples the first and the second coils to thesecondary recharge coil to recharge the rechargeable power source.

Another aspect relates to a method of recharging a rechargeable powersource of an IMD implanted within a patient. The method includesproviding a first coil and a second coil that lie in a first plane and asecond plane, respectively. The first and second coils are external tothe patient's body. The coils are positioned such that the IMD liesbetween the first and the second planes and the first and the secondplanes are substantially parallel to each other. A current is generatedin the first coil and the second coil to electromagnetically couple thefirst and the second coils to a secondary coil of the IMD to rechargethe rechargeable power source.

Other aspects of the invention will become apparent to those skilled inthe art from the following description and the accompanying Figures.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram of an Implantable Medical Device implanted in apatient.

FIG. 2 is a more detailed block diagram of an Implantable Medical Devicesituated under a cutaneous boundary with a recharging device positionedproximate to the cutaneous boundary.

FIG. 3 is a flux diagram illustrating that the flux density decreases asimplant depth increases.

FIG. 4A is a front perspective view of a lower portion of human torso inwhich an Implantable Medical Device is implanted.

FIG. 4B is a side view of human torso that corresponds to theconfiguration shown in FIG. 4A.

FIG. 5 is a flux diagram showing flux density relative to the torso ofFIGS. 4A and 4B.

FIG. 6 is a front perspective view illustrating one embodiment of anexternal recharging device that may be used to recharge a rechargeablepower source according to the current invention.

FIG. 7A is a front perspective view of a patient using a dual-coilrecharging device of a type similar to that shown in FIG. 6.

FIG. 7B is a back perspective view of patient of FIG. 7A employing thedual-coil recharging device.

FIG. 7C is a front perspective view of one embodiment of a coil holderof FIG. 7A.

FIG. 7D is a front perspective view of another embodiment of a coilholder.

FIG. 8A is a front view of one embodiment of a holster that may be usedto carry two coils according to the current invention.

FIG. 8B is a front view of the embodiment of the holster of FIG. 8A withthe shoulder strap over the patient's right shoulder.

FIG. 9A is a back view of a patient donning the holster of FIGS. 8A and8B.

FIG. 9B is a back view of the embodiment of the holster of FIGS. 8A, 8Band 9A.

FIG. 10 is a perspective view of a holster according to the embodimentof FIGS. 8A-9B.

FIG. 11A is a circuit diagram illustrating a pair of in-series coils.

FIG. 11B illustrates in-series coils that are similar to those shown inFIG. 11A but that each include multiple turns.

FIG. 12A is a perspective view of one embodiment of a torso strap thatmay be employed with an in-series coil configuration such as that shownin FIGS. 11A and 11B.

FIG. 12B is a perspective view of an alternative embodiment of the torsostrap shown in FIG. 12A.

FIGS. 13A and 13B are a front and back view, respectively, of a patientwho has donned a garment that covers the chest and torso according toone embodiment.

FIG. 13C is a view of another embodiment adapted to carry coilspositioned around the patient's head.

FIG. 13D is a view of an embodiment adapted to be positioned proximal toa patient's neck.

FIG. 13F is a side perspective view of an embodiment that carries afirst coil on a support structure on which the patient lies and anaccompanying item carrying a second coil that is adapted to cover thepatient as the patient is in the prone position.

FIG. 13G is an embodiment that carries the coils on a garment to bedonned on a lower portion of the patient's torso.

FIG. 14A is a front view of a patient in which an Implantable MedicalDevice is implanted in an angled configuration.

FIG. 14B illustrates an embodiment of the current invention that isadapted to recharge an Implantable Medical Device that is angled in amanner similar to that shown in FIG. 14A.

FIG. 15 is a flux diagram illustrating flux lines generated by a pair ofcoils that encircle a portion of the patient's body.

FIG. 16 is one embodiment of a system that provides two in-series coilsthat encircle a patient's torso.

FIG. 17 is a cross-sectional exploded view of the two ends of the beltof FIG. 16 illustrating how these ends overlap when the belt is donned.

FIG. 18 is another embodiment of a system that provides dual coils foran angled implant.

FIG. 19 is another embodiment of a garment having two coils thatencircle a portion of the patient's body.

FIG. 20A is a band that carries two coils according to one embodiment.

FIG. 20B is a garment to be worn around the lower portion of a patient'storso according to an embodiment.

FIG. 21 is a flow diagram of one exemplary method of using the currentinvention.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 shows an exemplary IMD 2, which may be a neurostimulator,implanted in patient 4. For instance, the IMD may be implanted withinthe abdominal cavity at a depth of greater than 3 centimeters from thepatient's skin, which is considered a “deep-implant scenario”.Furthermore, IMD 2 may be angled such that a secondary recharge coilcontained within, or otherwise associated with, the IMD is not parallelto a surface, or “cutaneous boundary”, of the patient's body. Moreover,at a given point in time, the exact angle of the secondary recharge coilrelative to a cutaneous boundary may be difficult to determine. This isso because that angle may change slightly over time based on a patient'sposture and/or the surgical approach that was used during implant.

IMD 2 can be any number of medical devices such as an implantabletherapeutic substance delivery device, an implantable drug pump, acardiac pacemaker, a cardioverter or defibrillator, a device to deliverelectrical stimulation pulses for a neurological or muscular condition,a device to deliver electrical stimulation to alleviate pain, or anyother IMD for delivering therapy. This therapy may be delivered via oneor more therapy connections 6, which may be one or more leads and/orcatheters.

FIG. 2 is a block diagram of one embodiment of IMD 2. According to thecurrent invention, IMD 2 includes a rechargeable power source 50.Rechargeable power source 50 can be any of a variety of rechargeablepower sources including a chemically-based battery or a capacitor. Inone embodiment, rechargeable power source 50 is a lithium ion battery.Any other type of rechargeable battery suitable for powering an IMD maybe used according to the current invention.

Rechargeable power source 50 is coupled to a control module 52, whichincludes circuitry to control therapy delivered to the patient. Controlmodule 52 may include one or more microprocessors, application-specificintegrated circuits (ASICs), digital signal processors (DSPs),field-programmable gate arrays (FPGAs), discrete electronic components,state machines, sensors, and/or other circuitry.

Control module 52 is further coupled, and provides power, to therapymodule 54. Therapy module 54 delivers some form of therapy to a patient.This therapy may include controlled delivery of a substance and/orelectrical stimulation. For example, in one embodiment, therapy module54 may include one or more output pulse generators such as capacitiveelements, voltage regulators, current sources, and/or switches that arecoupled to rechargeable power source 50 directly or through controlcircuit 52. Therapy module 54 may deliver electrical pulses to patient 4via a combination of electrodes. Therapy module 54 is coupled to patient2 through one or more therapy connections 6 such as leads and/orcatheters.

In one embodiment, rechargeable power source 50 is coupled to asecondary coil 56 (shown in cross-section) through a charging regulationmodule 58. During a recharge session, a current is induced in secondarycoil 56 in a manner to be discussed below. This current is provided viaconnection 60 to charging regulation module 58, which controls thecharging of rechargeable power source 50.

Rechargeable power source 50, charging regulation module 58, controlcircuit 52, and therapy module 54 are generally contained in ahermetically sealed housing 62. Secondary coil 56 may be attached to, orpositioned on, an exterior surface of sealed housing 62 throughconnection 60. For instance, secondary coil 56 may be contained within asecond housing 64 that is positioned adjacent to sealed housing 62. Inan alternative embodiment, secondary coil 56 may be contained in housing62 along with the other electronics.

In one embodiment, a magnetic shield 66 may be positioned betweensecondary coil 56 and housing 62. The primary purpose of magnetic shield66 is to substantially increase the amount of energy captured by thesecondary coil. Magnetic shield 66 also protects rechargeable powersource 50, control circuit 52, therapy module 54 and charging regulationmodule 58 from electromagnetic energy when secondary coil 56 is utilizedto charge rechargeable power source 50.

FIG. 2 further illustrates an external recharging device 70 which may beused to recharge rechargeable power source 50. External charging device70 is coupled via cable 72 to an antenna 74 (shown in cross-section). Inan alternative embodiment, charging device 70 and antenna 74 may becombined into a single unit.

Antenna 74 includes a first primary coil 76 (“first coil”, shown incross-section). During a recharge session, primary coil 76 is positionedproximate to secondary coil 56 on an opposite side of cutaneous boundary77 (shown dashed). Charging device 70 generates a current in firstprimary coil 76. When first primary coil 76 is positioned proximate tosecondary coil 56, the current in primary coil 76 electromagneticallycouples this primary coil to secondary coil 56. In the currentembodiment, this electromagnetic coupling is inductive coupling,although other forms of coupling (e.g., RF coupling) are possible. Theelectromagnetic coupling results in a current being generated insecondary coil 56. This current is provided to charging regulationmodule 58, which controls a rate at which rechargeable power source 50is recharged.

Recharging device 70 drives primary recharge coil 76 via power source80. Power source 80 may be rechargeable. For instance, power source 80may include rechargeable batteries to allow a patient who is engaged ina recharge session to be somewhat ambulatory during this process. Inthis embodiment, a desktop charging device (not shown) which is coupledto an AC or DC power source (e.g., via a wall outlet) may be used toperiodically recharge power source 80 when recharging device 70 is notin use. In another embodiment, recharging device 70 may be coupleddirectly to a source of AC power, such as a standard wall outlet duringthe recharge session.

Recharging device 70 may further include a control circuit 82. Controlcircuit 82 initiates and controls recharging sessions with IMD 2.Control circuit 82 may include one or more microprocessors, FPGAs,ASICs, DSPs, microsequencers, discrete components, and/or otherelectronic circuit components.

According to one embodiment of the current invention, recharging device70 may be coupled to a second antenna 84 via cable 86. Antenna 84, likeantenna 74, includes a second primary coil 88 (“second coil”, shown incross-section). Power source 80 is capable of driving both of primarycoils 76 and 88 at the same time so that a current is produced in eachof the coils having the same amplitude, frequency, and phase. First andsecond primary coils 76 and 88, respectively, may be positioned in amanner that generates a higher flux density through secondary coil 56than would be created using only one of primary coils 76 or 88. As aresult, a more efficient recharge of rechargeable power source 50 may beachieved. This is discussed further below.

It will be appreciated that recharging device 70 and IMD 2 are merelyexemplary. Many alternative configurations are possible for both ofthese devices. For instance, both recharging device 70 and IMD 2 mayinclude telemetry coils and control circuits for supporting telemetrycommunication between the two devices. Moreover, the various logicalfunctions may be partitioned differently. For instance, the controlcircuit 52 and therapy module 54 of IMD 2 may be combined into a singlelogic block, and so on. Thus, the implementations shown in FIG. 2 are tobe considered illustrative in nature only.

In FIG. 2, secondary coil 56 is shown proximate to cutaneous boundary77, with the plane in which this coil lies being approximately parallelto cutaneous boundary 77. This allows a magnetic field generated by acurrent within first primary coil 76 to readily couple with secondarycoil 56. Efficient inductive coupling may be harder to achieve whensecondary coil 56 is farther away from cutaneous boundary 77 (e.g., morethan 3 centimeters away) and/or if the plane in which secondary coil 56lies is not parallel to cutaneous boundary 77. This results in lessefficiency energy transfer between first primary coil 76 and secondarycoil 56.

FIG. 3 is a flux diagram illustrating the magnetic flux lines producedby a 100-turn flat (i.e., “pancake”) coil 100 that is ten centimeters indiameter. This type of coil may be constructed of conductive wire formedof copper or some other conductive material, which may be stranded. Itwill be assumed coil 100 carries a current of 1 milliamp (mA). Forpurposes of this example, it will be assumed that coil 100, which isshown in cross-section, corresponds to first primary coil 76 ofrecharging device 70.

Coil 100 has a central major axis 108. A central major axis (“majoraxis”) refers to an axis that intersects the center of the coil and isperpendicular to the plane in which the coil lies.

In FIG. 3, X-axis 102 represents a cutaneous boundary. Coil 100 ispositioned in close proximity to, and substantially parallel with, thisboundary, as would occur when the coil is positioned on a patient's skinin preparation to initiate a recharge session. Implant depth isrepresented by Y-axis 104, and increases as one moves away fromcutaneous boundary 102.

FIG. 3 further includes flux lines (e.g., flux lines 106). As known inthe art, these flux lines indicate the relative strength and directionof the magnetic field at any given location relative to coil 100. Inparticular, the density of the flux lines (that is, the “flux density”)is proportional to the magnitude of the local magnetic field vector. Asmay be seen in FIG. 3, the flux density is highest close to the coil.For instance, at a point along axis 108 that is close to cutaneousboundary 102, such as that corresponding to an implant depth of 3 cm orless, the flux lines are relatively close together. At a distance of 3cm, for instance, the flux density is roughly 2000 nT. As such, if asecondary coil were positioned substantially at this location, as wouldoccur if an IMD were implanted relatively close to the skin, efficientinductive coupling would be achieved between coil 100 and this secondarycoil.

FIG. 3 further illustrates that the flux density decreases dramaticallyas implant depth increases. For instance, assume an IMD is positionedalong axis 108 at an implant depth of 20 centimeters, and lies within aplane roughly parallel to a plane carrying coil 100. This is representedby location 110. In this scenario, the flux density at the implantlocation 110 has been reduced to 180 nanoTeslas (nT), which is notadequate to support an efficient recharge session. Thus, a single“pancake” coil is not effective for recharging an IMD used in the typeof deep implant situation represented by FIG. 3.

The current invention provides several coil configurations that increaseflux density to improve recharge coupling efficiency for deep-implantscenarios, and situations wherein the secondary recharge coil of an IMDis not necessarily positioned in a plane parallel to the cutaneousboundary.

FIG. 4A is a front perspective view of a lower portion of human torso150. Assume an IMD 154 has been implanted within a patient representedby torso 150 at a deep-implant location that is more than 3 cm from anyadjacent cutaneous boundary of torso 150. That is, the distancerepresented by arrow 153 between an adjacent cutaneous boundary and theimplant location represented by line 152 is more than 3 cm.

A first coil 156 is positioned on a first side of torso 150, which inthis example is the front of torso. A second coil 158 (shown dashed) ispositioned on an opposing, or opposite, side of torso from the firstside. In this example, secondary coil 158 is positioned on a back sideof torso 150. Coils 156 and 158 are positioned so that the two planes inwhich the coils lie are substantially parallel to each other. Moreover,these coils may also be substantially parallel to a third plane in whichIMD 154 lies. Additionally, these coils may be roughly positioned sothat both coils share a major axis 160. As discussed previously, a majoraxis of a coil is an axis that substantially intersects the center ofthe coil and which is perpendicular to the plane in which the coil lies.In one specific embodiment, the coils may be positioned so that majoraxis 160 intersects IMD 154. According to one aspect, major axis 160 maysubstantially coincide with a major axis of a secondary coil of IMD 154.

Currents induced in the clockwise direction of both coils 156 and 158result in magnetic flux lines 162 that are roughly perpendicular to theplane in which IMD 154 lies. Moreover, the flux density at IMD 154 thatis produced by the two coils 156 and 158 is much greater than thatproduced if only a single coil were employed. This is discussed in moredetail in relation to FIG. 5.

FIG. 4B is a side view of human torso 150 that corresponds to theconfiguration shown in FIG. 4A. Coil 156 (shown in cross-section) ispositioned proximate the front of torso 150, and coil 158 (also shown incross-section) is positioned proximate the back of torso 150. Whencurrent is induced in both coils in a clockwise direction in the mannershown in FIG. 4A, magnetic flux is produced that flows through themiddle of both coils from the front to the back of torso 150. These fluxlines 162 flow through IMD 154 (shown in cross-section), and wouldinductively couple with a secondary coil lying in the plane of IMD 154.Returning flux lines 166 flow from secondary coil back to primary coil,completing the magnetic circuit. Using this configuration, the densityof flux lines 162 coupling with the secondary coil of IMD issignificantly greater than would be achieved if only a single coil wereused.

FIG. 5 is a flux diagram illustrating the magnetic flux lines producedby two coils that are each similar to the coil employed to produce thediagram of FIG. 3. That is, each of the coils is a 100-turn pancake coilthat is ten centimeters in diameter and carries a current of 1 mA.

FIG. 5 represents flux flowing through a cross section of torso 150, theoutline of which is indicated by outline 200. Coils 202 and 204 (shownin cross-section) are positioned at cutaneous boundaries 206 and 208,respectively, of torso outline 200. This represents the scenario whereincoils 202 and 204 are located on opposing sides of the torso, which inthis example are the front and back of a torso, respectively. Thiscorresponds to the positioning of coils 156 and 158 on torso 150 ofFIGS. 4A and 4B. In another embodiment, it is possible to position thecoils on opposing sides of torso, rather than the torso front and back.

Major axis 210 intersects the centers of both coils 202 and 204 and issubstantially perpendicular to the planes that carry these coils. Thedistance between the centers of coils 202 and 204 along axis 210 is 40cm, as indicated by arrows 214. A position 212 may be identified alongline 210 that is equidistant from the centers of both coils. That is,position 212 is roughly 20 cm from the center of each of the coils, asshown by arrows 214. At this position, the flux density is roughly 305nT. This is considerably greater than the flux density of 180 nT thatwould be achieved if either coil 202 or 204 were used alone. Thus, theuse of dual pancake coils positioned on the front and back of the torsogreatly increases the flux density at a deep implant position locatedalong a line that intersects the centers of the coils, such as position212 that is roughly equidistant from the center of both the coils.

FIG. 6 is a front perspective view illustrating one embodiment of anexternal recharging device 250 that may be used to recharge arechargeable power source according to the current invention. Externalrecharging device 250 is coupled to first and second primary coils 252and 254 via cables 256 and 258, respectively. Electronics withinexternal recharging device 250 drive coils 252 and 254 via separateports 253 and 255, respectively, to produce a current. In oneembodiment, the current generated in coil 252 has the same frequency,phase and amplitude as that generated in coil 254. Coils 252 and 254 maybe positioned on opposites sides (e.g., a front and a back, or a leftand right side) of torso, respectively, in the manner shown in FIGS. 4A,4B, and 5 to increase the flux density produced at a deep-implantlocation such as one that is approximately more than 3 cm from eithercoil.

Controls 260 are provided on the front of recharging device 250 to allowa patient or a clinician to initiate and control the recharging of animplanted IMD. In one embodiment, recharging device 250 supports a firstmode wherein recharging device generates a current in a selected one ofcoils 252 and 254. This allows a single one of coils 252 or 254 to beused to recharge a rechargeable power source carried by an IMD locatedrelatively close (e.g., roughly 3 cm or less) from a cutaneous boundary.A second mode is provided wherein recharging device 250 generates acurrent in both coils in the manner discussed above to recharge an IMDimplanted more deeply within the body. Status regarding operation ofrecharging device 250 may be provided via display screen 262.

FIG. 6 further illustrates an optional recharger holder 264 thatreceives recharging device 250. Holder 264 may be fashioned to include acutaway portion 266 that allows a patient to access controls 260. Asecond cutaway portion 268 may be provided to allow a patient to viewdisplay screen 262 of recharging device 250. A third cutaway portion 270may be provided to allow cables 256 and 258 to couple to rechargingdevice 250. During a recharge session, recharger holder 264 may becoupled to a strap, belt, or some other support member carried on, orworn by, the patient (not shown in FIG. 6). Alternatively, rechargingdevice 250 may be carried in a pocket of the patient's clothing, orattached to a hook or some other support member carried on, or worn by,the patient without the use of recharger holder 264.

FIG. 7A is a front perspective view of a patient 301 using a dual-coilrecharging device of the type shown in FIG. 6. The patient has donned atorso strap 300 (e.g., a belt), which may be formed of any durableflexible material such as nylon, cotton, leather, and the like. Torsostrap 300 may be retained around the patient's torso via any type offastener, such as hook-and-eye strips (e.g., VELCRO® fasteners),buckles, snaps, belts, ties, buttons, and so on. Torso strap 300 engagesor otherwise carries a first coil holder 302 (“first holder”). In oneembodiment, first holder 302 slidably engages torso strap 300, as may beaccomplished by threading torso strap 300 through slots included insides of first holder 302. In this manner, first holder 302 may beslidably positioned along torso strap 300 to a selected location that isproximate to an implant location, as will be discussed below. When sopositioned on the torso strap, first holder 302 forms a pocket that issized to receive one of coils 252 or 254 of recharging device 250.

Torso strap 300 may also be coupled to recharger holder 264 (FIG. 6), asmay be accomplished via a belt clip, hook, or some other supportmember(s). Recharger holder 264 carries recharging device 250, which isshown coupled to cables 256 and 258. Cable 256 is, in turn, coupled tocoil 252 in the manner shown in FIG. 6. Coil 252 is inserted into thepocket formed between first holder 302 and torso strap 300.

FIG. 7B is a back perspective view of patient 301 of FIG. 7A. Torsostrap 300 encircles the torso of the patient. Cable 258, which iscoupled to recharging device 250 in the manner shown in FIG. 7A,encircles the patient's right side and is coupled to coil 254. Coil 254is inserted within a second holder 304. Like first holder 302 of FIG.7A, second holder 304 forms a pocket with torso strap 300 that is sizedto receive coil 254. In one embodiment, second holder 304 includes slotsalong its side through which torso strap 300 is threaded. Second holder304 may thereby be slidably positioned along belt to a selectedlocation. By positioning first and second holders 302 and 304 alongbelt, they may be aligned substantially as shown in FIGS. 4A, 4B, and 5.That is, the major axis that intersects the centers of coils 302 and 304also intersects an IMD implanted within patient 301. Recharging device250 may then be used to generate a current within coil 252 that has thesame frequency, amplitude, and phase as that generated within coil 254.This produces a flux density at the implant location in a manner similarto that shown in FIG. 5. This flux density is sufficient to support anefficient recharge session to recharge a rechargeable power sourcecontained within the IMD, even when IMD is situated at a deep-implantlocation.

FIG. 7C is a front perspective view of one embodiment of first holder302 of FIG. 7A. A similar configuration may be used for second holder304 of FIG. 7B. Holder 302 includes side portions 350 and 352, which maybe constructed of a durable material such as polyurethane. Side portions350 and 352 include slots 354 and 356, respectively, to receive torsostrap 300.

Each of side portions 350 and 352 are coupled to a flexible strap 358which may be made of nylon, leather, cotton, or some other suitablematerial. Strap 358 may be coupled to a clip 360 or some other supportmember provided to support coil 252 in the manner shown. Alternatively,coil 252 may be held in position solely by threading torso strap 300through slots 354 and 356 and tightening the belt such that belt andstrap 358 exert pressure on coil 252.

FIG. 7D is a front perspective view of another embodiment of a coilholder suitable for use as first and second holders 302 and 304 of FIGS.7A and 7B. In this embodiment, the coil holder is a pouch 370 of a typethat may be configured from a material such as nylon, cotton, leather,or any other durable fabric. Pouch 370 is sized to receive coil 252.Pouch includes a mechanism for connecting it to torso strap 300, such asvia one or more clips, hooks, snaps, ties, buttons, hook-and-loopfastening strips, and/or any other support member(s). Alternatively,slots or belt loops may be provided in pouch 370 through which torsostrap 300 may be threaded in a manner similar to that discussed inregards to FIG. 7C. Preferably, the connecting mechanism allows forselective positioning of the pouch along torso strap 300.

In yet another embodiment, some type of fastening member may be coupleddirectly to, or provided by, coils 252 and 254. For instance, each coilmay be integrally formed with a belt clip or other fastener that isprovided to couple the coils directly to the torso strap without use ofan additional holder.

In FIGS. 7A-7D, coils 252 and 254 are shown carried in pocketsassociated with torso strap 300. In this type of embodiment, belt mustbe positioned at a height that corresponds substantially with the heightof the implant within a patient's body. In some situations, this may beundesirable. For instance, implant may be positioned within theabdominal cavity in a location that is adjacent to a patient's rib cage.In this instance, it may not be comfortable to encircle torso strap 300around the torso at the same height as the implant. In this case, coils252 and 254 may be carried in pockets associated with a shoulder strap.

FIG. 8A is a front view one embodiment of a holster that may be used tocarry coils 252 and 254 according to the current invention. In thisembodiment, a torso strap 400 encircles torso of patient 402. Torsostrap 400 is maintained around the patient's torso by a fastener 404,which may be a clip, a buckle, hook-and-loop fasteners, or any othertype of fastening device.

Torso strap 400 engages a shoulder strap 406. For example, an end ofshoulder strap 406 may be configured to form a loop 408 that slidablyengages torso strap 400. Shoulder strap 406 extends over a shoulder ofpatient 402 to the patient's back. Shoulder strap 406 carries a firstcoil holder 410 (“first holder”) which may be a pocket formed of adurable, flexible material such as nylon, cotton, or leather, and isadapted to hold a respective one of coils 252 and 254 of rechargingdevice 250 (FIG. 6). In FIG. 8A, first holder 410 is shown to hold coil252, which is coupled to cable 256. In one embodiment, first holder 410may have a tab 411 that can be readily grasped to pull open the pocketand insert one of coils 252 and 254. First holder 410 of one embodimentmay be selectively positionable relative to shoulder strap 406. This isdiscussed further below. According to one aspect, first holder 410 maybe configured in a manner described by commonly-assigned U.S. patentapplication entitled “Holster for Charging Pectorally-Implanted MedicalDevices”, U.S. patent application Ser. No. 12/061,055, filed Apr. 2,2008.

Torso strap 400 may be further coupled to recharger holder 264, as maybe accomplished via a belt clip, some other type of fastener, or viaslots within the recharger holder through which torso strap may bethreaded. Recharge holder 264 supports recharging device 250, which iscoupled via cable 256 to coil 252, which is shown inserted within firstholder 410. Recharging device 250 is further coupled to cable 258, whichextends to second coil 254 (not shown in FIG. 8A).

FIG. 8B is a front view of the embodiment of the holster of FIG. 8A withshoulder strap 406 having been donned over the patient's right, ratherthan left, shoulder. In FIGS. 8A and 8B, like elements are designatedwith the same numeric identifiers. As was the case in FIG. 8A, loop 408may be slid along torso strap 400 to further adjust the lateral (i.e.,horizontal) position of coil holder 410.

FIG. 9A is a back view of patient 402 and the holster of FIGS. 8A and8B. In particular, the holster has been donned over the patient's leftshoulder in the manner shown in FIG. 8A and engages torso strap 400. Inone embodiment, this is accomplished by providing a loop 412 at a backend of shoulder strap 406. Loop 412 receives, and slidably engages,torso strap 400. In other embodiments, shoulder strap 406 may engagetorso strap 400 in a different manner such as with hooks, ties,hook-and-loop strips, or other fastening means.

Shoulder strap 406 carries a second coil holder 414 (“second holder”)which is adapted to support or receive one of coils 252 and 254 ofrecharging device 250 (FIG. 6). Second holder 414 may be a pocket formedout of a durable flexible material such as nylon, cotton, or leather,for instance. Second holder 414 may have a tab 415 that may be graspedto spread the pocket of holder so that a coil may be readily inserted.For instance, the holder may be fashioned in a manner similar to thatdescribed in the commonly-assigned U.S. patent application entitled“Holster for Charging Pectorally-Implanted Medical Devices” referencedabove. In one embodiment, second holder 414 may be selectivelypositionable relative to shoulder strap 406, as will be discussed below.

In FIG. 9A, second holder 414 carries coil 254, which is coupled tocable 258. Cable 258 extends around the patient's left side and isconnected to recharging device 250 in the manner should in FIG. 8A.

FIG. 9B is a back view of the embodiment of the holster of FIGS. 8A, 8Band 9A. In FIGS. 8A, 8B, and 9A, like elements are designated with thesame numeric identifiers. In FIG. 9B, shoulder strap 406 is shownpositioned over the patient's right, rather than left, shoulder in amanner that corresponds to that shown in FIG. 8B. Loop 412 may be slidalong torso strap 400 to further adjust the lateral position of secondholder 414. In this embodiment, second holder 414 carries coil 254,which is coupled to cable 258. Cable 258 encircles the patient's leftside in the manner shown in FIG. 8B.

In a preferred embodiment, coils 252 and 254 are carried within coilholders 410 and 414. The position of coils relative to a patient's torsois highly adjustable. In particular, the lateral (i.e., horizontal)position of coils is adjusted by positioning shoulder strap 406 relativeto torso strap 400. In one embodiment, this is accomplished by slidablypositioning loops 408 and 412 along torso strap 400. In addition, theheight of coil holders 410 and 414 may be adjusted along shoulder strap406 to accommodate an implant that is located above a patient'swaistline. The position of first and second holders 410 and 414 may beadjusted so that coils 252 and 254 will share a same major axis when thecoils are carried by the holders. Moreover, the position of holders maybe adjusted so that this major axis substantially coincides with a majoraxis of secondary coil of an IMD implanted within patient 402. This isas shown in FIGS. 4A, 4B, and 5. This allows for efficient recharging ofan IMD that is located at a deep-implant location within patient 402.

FIG. 10 is a perspective view of a holster according to the embodimentof FIGS. 8A-9B. In FIGS. 8A-10, like elements are designated with thesame numeric identifiers. Torso strap 400 is shown coupled to a fastener404. Fastener 404 of the illustrated embodiment includes a femaleportion 404A that receives and engages a male portion 404B. Male portion404B includes an adjuster 452 through which end 454 of torso strap 400is threaded. The length of torso strap 400 is adjusted according to thegirth of patient 402 by pulling on end 454.

Shoulder strap 406 engages belt via two slidable loops 408 and 412.Shoulder strap 406 includes first and second holders 410 and 414. In theillustrated embodiment, coil holders 410 and 414 are fashioned byaffixing multiple layers of fabric together as by one or more rows ofstitching 456. This forms a pocket that may be accessed by grasping oneof tabs 411 and 415 to spread the corresponding pocket. For instance,FIG. 10 illustrates tab 411 folded back to expose the pocket of firstholder 410. A similar pocket is provided by second holder 414. Thepocket is sized to receive one of coils 252 and 254. For instance, coil252 may be inserted into first holder 410, as indicated by arrow 457.Similarly, coil 254 may be inserted into second holder 414, as indicatedbe arrow 458.

In one embodiment, shoulder strap 406 includes several adjusters toadjust the length of shoulder strap to fit the length of a patient'storso, as well as to adjust the position of first and second holders 410and 414, respectively, relative to shoulder strap 406. For instance,adjuster 462 is provided to adjust the height of coil holder 410. Inparticular, a middle bar of adjuster 462 is coupled to a strap 464 thatis folded to provide loop 408. Adjuster 462 further includes two slotsthrough which strap 460 is threaded. By adjusting the position of strap460 relative to adjuster 462 (e.g., by pulling on end of strap 460), theheight of first holder 410 can be adjusted downward or upward relativeto torso strap 400.

A similar adjuster 466 is provided to adjust the length of shoulderstrap 406. Adjuster 466 includes a middle bar that is coupled to a strap467 of holder 410. Adjuster 466 includes slots through which an end 468of an intermediate strap 470 is threaded. By adjusting the position ofstrap 470 relative to adjuster 466, the length of intermediate strap 470may be altered to meet a patient's torso length. Alternatively, oradditionally, an adjuster 472 may be provided having slots that receiveanother end 474 of intermediate strap 470 in a manner similar to thatshown for adjuster 466. Adjusting end 474 relative to the position ofadjuster 472 likewise adjusts the length of intermediate strap 470 tothe length of a patient's torso.

Yet another adjuster 476 may be provided that is similar to adjuster462. That is, adjuster 476 includes a middle bar that is coupled to astrap 478 that is folded to provide loop 412. Adjuster 476 furtherincludes two slots (not visible in FIG. 10) that receive strap 480. Byadjusting the position of strap 480 relative to adjuster 476 (e.g., bypulling on an end of strap 480) the position of second holder 414 may beadjusted relative to torso strap 400.

The embodiment of FIG. 10 provides a highly adjustable system that maybe used to optimally recharge a rechargeable power source carried by anIMD when the IMD is situated at a deep-implant location within apatient's body. The length of torso strap 400 may be altered viaadjuster 452 to fit a patient's girth. The position of coils 252 and 254may be adjusted laterally (e.g., horizontally) relative to a person'storso by sliding loops 408 and 412 of shoulder strap 406 along torsostrap 400. The height of coils may also be positioned vertically viaadjusters 462, 466, 472, and 476 in a manner discussed above. Theseadjusters also allow the length of intermediate strap 470 to be adjustedto fit the length of a patient's torso. In this manner, each of coils252 and 254 may be adjusted in each of two dimensions so that the coilsmay be aligned to share a major axis which, in one embodiment,intersects with a center of an IMD implanted within the patient.Optimally, the shared major axis substantially coincides with a majoraxis of the IMD in the manner illustrated in FIGS. 4A and 4B.

The embodiments discussed above contemplate a system that utilizes twopancake coils that are driven separately by respective ports of arecharging device such that a current having the same amplitude,frequency, and phase are generated in each of the coils. Anotheralternative embodiment utilizes a pair of circular coils having the samenumber of turns, the same diameter, and that are positioned along acommon axis. The coils are electrically connected in series such that acurrent flowing in one of the coils also flows in the other coil.

FIG. 11A is a circuit diagram illustrating a pair of in-series coils.The coils are coupled in series with one another via an intermediateconductor 508 such that the same current generated in coil 500 willlikewise be generated in coil 502. Conductors 509A and 509B are coupledto, or integral with, coils 502 and 500, respectively. Conductors 509Aand 509B are carried back to, and are coupled with, a recharging devicevia cable 510. This allows the recharging device to drive the in-seriescoil pair with a current.

Before continuing, it is noted that the foregoing discussion refers tovarious conductors 508, 509A, and 509B, as well as coils 500 and 502 asthough they are formed of different conductors. These structures are, inone embodiment, formed of the same conductor (e.g., wire) that is shapedinto a configuration similar to that shown in FIGS. 11A and 11B. Thereference to these various conductors is for ease of description only,and it is therefore to be understood that all of the referencedconductors may be integral to one another.

In one embodiment, coil 500 lies in a first plane that is substantiallyparallel to a second plane in which coil 502 lies. In a more specificembodiment such as that shown in FIG. 11A, the two coils share a majoraxis 506. As discussed above, a major axis is an axis that intersectsthe midpoint of the coil and that is also perpendicular to a plane inwhich the coil lies.

FIG. 11B illustrates in-series coils that are similar to those shown inFIG. 11A, except that each of the coils includes two turns. It will beunderstood that for an in-series coil pair, each of the coils mayinclude any number of turns, as long as both coils are the same. FIG.11B further illustrates flux lines 511 that are produced by the coilswhen a current is flowing in the counter-clockwise direction in bothcoils. A current may instead be generated in the opposite direction, ifdesired.

IMD 512 is located between the two coils. In one embodiment, a majorplane of the IMD (that is, a plane intersecting the IMD and which isparallel to the largest surface of the IMD) is substantially parallel tothe first and second planes in which the first and second coils,respectively, lie. IMD 512 may be located at an approximate mid-pointbetween the two coils, or at some other point between the two coils. Inthis manner, a secondary coil that is carried by, and lies in the majorplane of, the IMD will be optimally positioned to intercept flux lines511 so that an efficient recharge session may be conducted.

FIG. 12A is a perspective view of one embodiment of a torso strap 550that may be employed with an in-series coil configuration such as thatshown in FIGS. 11A and 11B. Torso strap 550 is adapted to encircle atorso of a patient. Torso strap 550 includes a fastener 552 used toretain the belt around the patient's torso. In the illustratedembodiment, fastener 552 is a buckle that includes a female portion 552Athat engages a male portion 552B, although any other type of fastenermay be utilized, including a buckle, hook-and-loop strips, hook-and-eyemechanisms, snaps, ties, buttons, and so on.

In the illustrated embodiment, male portion 552B of fastener 552includes an adjuster 556. An end 554 of torso strap 550 is threadedthrough adjuster 556. By adjusting the position of end 554 relative toadjuster 556, torso strap 550 is adjusted to fit the girth of apatient's torso.

Torso strap 550 includes first and second holders 560 and 562 thatslidably engage torso strap 550. For instance, each holder may be formedby wrapping a strap of flexible durable material such as nylon, cotton,or leather around torso strap 550 and affixing the strap to itself toform a loop. Each of the first and second holders 560 and 562 carries arespective one of the in-series coils. For instance, coil 500 of FIG.11A (shown dashed in FIG. 12A) may be carried on, or by, an innersurface of first holder 560. Similarly, coil 502 of FIG. 11B (notvisible in FIG. 12A) may be carried on, or by, an inner surface ofsecond holder 562.

Coils may be affixed to, or otherwise carried on, a respective holder ina number of ways. For instance, a coil may be held in place on a surfaceof a holder, or may instead be retained between multiple layers offabric of a holder using multiple rows of stitching, adhesive, or someother fastening mechanism.

The in-series coils 500 and 502 are coupled to one another by variouscable portions 564, 566, and 568. Cable portions 564 and 566 carryintermediate conductor 508 to, and conductor 509B (FIG. 11A) from, coil500. Likewise, cable portion 564 carries intermediate conductor 508 tocoil 502 (not visible), which is on an inner surface of holder 562.Cable portion 568, which is an extension of cable 564, carries conductor508 to, and conductor 509A (FIG. 11A) from, coil 502. Cable 570 carriesconductors 509A and 509B back to recharging device 572. As discussedabove, all of these conductors may, in fact, be part of, or formed from,the same conductor (e.g., the same wire) and referencing these variousconductor structures is for ease in understanding how the in-seriescoils 500 and 502 are carried by torso strap 550.

Cable portion 564 is carried in a fixed manner on torso strap 550. Forinstance, this cable portion 564 may be held in place between fabriclayers via rows of stitching. Alternatively, cable portion 564 may beaffixed in place with adhesive, or using any other suitable manner.

In one embodiment, cable portions 566 and 568 are provided as extensionof cable 564, and are left unattached to the torso strap to allow firstand second holders 560 and 562 to move laterally (i.e., horizontally)along the front and back of torso strap 550. This allows the position ofcoils 500 and 502 to be adjusted laterally. By adjusting the position ofcoil holders 560 and 562 in this manner, and by further adjusting theheight of torso strap 550 around a patient's torso, the coils may bealigned so that they share a major axis, and that this shared major axisintersects an implanted IMD. Optimally, the shared major axis intersectsa major axis of the secondary coil of the IMD.

Cable 570 connects coils 500 and 502 and intermediate conductor 508 to arecharging device 572. This recharging device may be fastened to torsostrap 550 using a belt clip, a holder such as holder 264 of FIG. 6, orby some other fastening mechanism. During a recharge session, rechargingdevice 572 generates a current in coils 500 and 502 so that flux lines574 are produced. These flux lines will intersect an IMD that is locatedbetween coils 500 and 502 to efficiently recharge a device residing at adeep-implant location.

FIG. 12B is a perspective view of an alternative embodiment of the torsostrap shown in FIG. 12A. In FIGS. 12A and 12B, like elements areidentified with like numeric designations. In this embodiment, two coilholders 580 and 582 are provided. Coil holder 580 carries pocket 584,and coil holder 582 carries a similar pocket 586 (shown dashed). Thepockets 584 and 586 are each sized to receive a coil having someselected maximum diameter. The pockets can thereby receive coils of thismaximum diameter, or coils having a smaller diameter. For instance,pocket 584 is shown carrying coil 588 and pocket 586 carries coil 590.In one embodiment, coils 588 and 590 are the same size and will alsohave the same number of turns and electrical properties. In oneembodiment, connectors 589 and 591 are provided so that coils ofdifferent sizes may be removably coupled to cable portions 566 and 568.

In another embodiment, the entire coil assembly is removably coupled totorso strap 550. In this embodiment, cable portion 564 is made to beremovably affixed to torso strap 550, as by a plastic groove included onthe inner surface of torso strap 550 that is sized to receive cableportion 564, as by allowing it to snap into position in the groove.Alternatively, hook-and-loop fastener strips, hooks, ties, or some othercoupling mechanism may be used to affix cable portion 564 to the innersurface of torso strap 550. In this manner, coils 588 and 590 may beselected based on a desired coil diameter.

The foregoing figures provide various embodiments of torso straps and/orshoulder straps for retaining the first and second coils in placerelative to a patient's body. It will be understood that many otherembodiments are possible within the scope of the current invention.

FIGS. 13A and 13B are a front and back view, respectively, of a patientwho has donned a garment 592 that covers the chest and torso. Thisgarment may be a shirt, sweater, vest, and so on. This garment carries afirst coil 594 (shown dashed) that has been affixed, or otherwisesupported, by garment 592. For instance, the coil may be stitched intothe fabric, attached via adhesive or any other fastening means known inthe art, supported by a pocket, etc. Coil may be provided on theunderside of the garment (as indicated by dashed lines) to allow forbetter coupling with the patient's skin. Coil 594 has been coupled to arecharging device 593, which may be supported by a pocket of thegarment. A second coil 595 (shown dashed), which is likewise coupled torecharging device 593, is carried on the backside of the garment, asshown in FIG. 13B. The two coils are arranged so that they are onopposing sides of the body. In one embodiment, the coils share a majoraxis.

A garment such as shown in FIGS. 13A and 13B may be adapted to carry thecoils anywhere on the garment. For instance, the coils may be carried onthe sides of the garment so that they are located substantially underthe arms of the patient. This configuration may be selected to rechargean IMD that has a secondary recharge coil that lies in a planesubstantially parallel to the sides of the patient's torso.Alternatively, the coils may be carried at a higher or lower position onthe garment based on the location of the IMD within the patient. In oneembodiment, the entire garment could include hook-and-loop fasteningstrips that are provided to receive opposing strips on the coils so thatthe coils may be selectably repositioned anywhere on the garment. Thisallows one garment design to be suitable for use by different patientshaving different implant locations.

FIG. 13C is a view of another embodiment adapted to carry coilspositioned around the patient's head. In this embodiment, a cap carriescoils 596 and 597 (shown dashed), which may be affixed to the cap in anymanner known in the art, including using those mechanisms mentionedabove. The coils may be positioned on any two opposing sides of the cap(e.g., front and back, left and right, etc.). These coils may beprovided on the underside of the cap to provide better coupling to thepatient. Other headwear may be used instead of a cap to carry the coils,including any type of hat, or a headset of the type that may be used tolisten to portable audio devices. This embodiment is suitable torecharge an IMD implanted within a patient's head.

FIG. 13D is a view of an embodiment adapted to be positioned proximal toa patient's neck. This neckwear may be similar to inflatable braces usedby travelers to aid in relaxation during a long trip. The neckwear maybe formed of foam or any other material that is capable of holding itsshape yet is comfortable during use. The neckwear consists of a supportmember having an opening that receives a person's neck. When the neck isso positioned with the opening, the neckwear surrounds the neck aroundthe back and sides of the neck. Coils 598 and 599 are carried on theinner surface of the opening so that they are proximal to the sides ofthe neck. The coils are adapted to most efficiently recharge an IMDhaving a secondary coil that lies in a plane substantially parallel tothe sides of the neck.

A variation of the neckwear provides an opening that opens on a firstside of the neck so that when the neckwear is donned, it surrounds theneck on the front, back, and the second side of the neck. The coils maythen be positioned proximal to the front and back of the neck torecharge an IMD having a secondary coil that is located in a planesubstantially parallel to the front and back of the patient's neck.

FIG. 13F is a side perspective view of an embodiment that carries afirst coil 601 on a support structure 600 on which the patient lies anda second coil 604 carried by an item 603 that covers the patient. Forinstance, the support structure 600 that carries the first coil may be amattress pad, a blanket, a sleeping bag, a sofa cushion, or any otherstructure on which the patient may lie. The item that covers the patientmay be a blanket, sheet, or any other item adapted to be positioned overthe patient. Coils 601 and 604 may be aligned so that they share a majoraxis. Further, they may be aligned so that this major axis intersects,or even shares a major axis with, an implanted IMD within the patient.Current is then generated in the coils by recharging device 602.

In one embodiment, support structure 600 and item 603 may beincorporated into a single structure. For instance, a sleeping bag maybe provided that carries the coils on opposite sides of the bag (e.g.,top and bottom, left and right side, etc.) When the patient is insidethis structure, the coils are then substantially aligned on opposingsides of the patient's body. The configuration of the structure isselected based on the patient's particular implant scenario.

FIG. 13G is an embodiment that carries the coils on a garment to bedonned on a lower portion of the patient's torso. For instance, thegarment may be pants, shorts, a skirt, and so on. In this example, coil605 (shown dashed) is shown positioned on the front of the garment. Asimilar coil (not shown) is positioned on the back of the garment. Inone implementation, this second coil is located so that it substantiallyshares a major axis with coil 605. The coils are thereby provided foruse with an IMD implanted in a lower portion of the patient's torso. Ifdesired, the coils may be positioned in the leg portion of the garmentto recharge an IMD implanted in the patient's leg.

The various embodiments discussed above may be best suited for anapplication wherein the secondary coil of the IMD is located within aplane that is roughly parallel to the planes that carry the coils.However, when the secondary coil of the IMD is in a plane that isangled, the foregoing embodiments may not be as effective in recharginga power source carried by the IMD. This is because most of the fluxlines generated by embodiments such as those discussed above will not beintercepted by a secondary recharge coil that is associated with, andsubstantially in the plane of, the IMD.

FIG. 14A is a front view of a patient in which an IMD 612 is implantedin an angled configuration. The IMD is located within a plane that issubstantially perpendicular to the front, the back, and both sides ofthe patient's torso. In this type of scenario, the embodiments discussedabove may result in diminished recharge efficiency.

FIG. 14B illustrates an embodiment of the current invention that isadapted to recharge an implant that is angled in a manner similar tothat shown in FIG. 14A. This embodiment utilizes two coils that encirclea patient's torso to perform recharge of the angled implant. A firstcoil 613 and a second coil 614 are wrapped around the patient's torso.The coils may, but need not, be electrically connected in series via anintermediate conductor 616. This in-series configuration is similar tothe orientation of the two in-series coils shown in FIGS. 11A and 11B. Acounter-clockwise current induced in the coils will generate flux in thedirection shown by flux lines 618. This flux optimally intersects aplane in which IMD 612 lies, which is substantially perpendicular to theflux. Thus, an efficient recharge session may be conducted for a devicethat is angled within the patient.

FIG. 15 is a flux diagram illustrating flux lines generated by a pair ofcoils 620 and 622 (each shown in cross-section) that may beconceptualized as encircling a patient's torso in a manner similar tothat shown in FIGS. 14A and 14B. In this diagram, these coilssubstantially share a major axis 624. As discussed above, a major axisintersects a center of the coils and is perpendicular to the plane inwhich the coil lies.

This example represents the situation wherein major axis 624 parallelsthe length of the patient's spine, with the patient being encircled bythe coils. The front, back, and sides of a patient's torso would also begenerally parallel to axis 624. The flux lines of FIG. 15 are generatedby two coils that are 10 cm apart having a diameter of 50 cm andincluding 20 turns. In one embodiment, the coils are formed of copperlitz wire, type 20-26 American Wire Gauge (AWG). When a current of 1 mAis induced in the coils 620 and 622, a flux density of 305 nT isgenerated at a location 626 that is equidistant from each coil and thatis roughly 5 cm from axis 624. This represents an implant depth of about20 cm, as indicated by arrow 628.

As is apparent from the foregoing, for an implant depth of about 20 cm,two 20-turn coils having a diameter of 50 cm and that are positionedaround a patient's waist in the manner represented by FIG. 15 generatethe same flux density as two 100-turn coils having a diameter of 10 cmthat are positioned on the front and back of a patient's torso in themanner represented by FIG. 5.

FIG. 16 is one embodiment of a system that provides two in-series coilsthat encircle (that is, wrap around) a patient's torso in a mannersimilar to that shown in FIGS. 14A, 14B, and 15. A belt 630, which mayalso be described generally as a torso strap, is formed of a durablestrip of material such as nylon, cotton, leather or some type of fabric.Belt 630 is sized to fit around a patient's torso when a first end 632of the belt 630 is positioned to overlap the other end 634 (showndashed) in the manner illustrated in FIG. 16.

Belt 630 carries one or more conductors along a lower edge, and an equalnumber of conductors along an upper edge. For instance, in theillustrated embodiment, three conductors 636, 638, and 640 extendapproximately the entire length of belt along the lower edge. Similarly,conductors 646, 648, and 650 extend approximately the entire length ofbelt 630 along the upper edge. As one example, these conductors may beformed of copper litz wire, type 20-26 AWG, although other types ofconductors may be used in the alternative. These coils may be affixed tothe belt using stitching, adhesive, or some other suitable mechanism.

At end 632, conductors 638 and 640 are each electrically coupled to anelectrical via 642. Each of the vias 642 extends through to theunderside of belt 630 and electrically couples to, or is integral with,a respective male contact member (not visible in FIG. 16) that is formedof an electrically conductive material. An additional via 644 isprovided that electrically couples to, or is integral with, anadditional male contact member in the manner discussed above.

At end 634 of belt, each of conductors 636, 638, and 640 is electricallycoupled through to a female fastening member that is on the front sideof belt 630 (not visible in FIG. 16). When belt 630 is configured in aloop as to encircle a patient's torso in the manner shown in FIG. 16,each of the female contact members on the front side of end 634 of belt630 may be electrically coupled with a corresponding one of the malecontact members provided at the underside of the belt at end 632. Forinstance, via 642 of conductor 638 extends through belt 630 to a malecontact member on the underside of belt which is provided to couple to afemale contact member of conductor 636 that is located at end 634.Similarly, via 642 of conductor 640 extends through belt to a malecontact member which is adapted to mate with a female contact member ofconductor 638. Finally, via 644 extends to a male contact member, whichcouples to a female contact member of conductor 640. In this way, thethree conductors 636, 638, and 640 are electrically coupled in a serialmanner to form a three-turn coil when the electrical contacts are madebetween the male contact members located on the underside of end 632 andthe female contact members on the front side of end 634.

In a similar manner to that described above, at end 632, conductors 648and 650 are each electrically coupled to a respective one of vias 652.Each of the vias 652 extends through to the underside of belt 630 andelectrically couples to, or is integral with, a respective male contactmember that is formed of an electrically conductive material. Anadditional via 654 is provided that electrically couples to, or isintegral with, an additional male contact located on the underside ofthe belt in the manner discussed above.

At end 634 of belt, each of conductors 646, 648, and 650 is electricallycoupled to a female fastening member that is on the front side of belt630. Each of the female contact members at end 634 of belt 630 isprovided to electrically couple with a corresponding male contact memberthat is located at end 632 of belt 630. For instance, via 652 ofconductor 648 extends to a male contact member which is provided tocouple to a female contact member of conductor 646 located at end 634.Similarly, a via 652 of conductor 650 extends to a male contact memberwhich is adapted to couple to a female contact member of conductor 648.Finally, via 654 electrically couples through a male contact member to afemale contact member of conductor 650. In this way, the threeconductors 646, 648, and 650 are electrically coupled in a serial mannerto form a three-turn coil when the electrical contacts are made betweenthe male contact members located on the underside of the belt at end 632and the female contact members located on the front side of the belt atend 634.

Finally, a conductor 660 is provided to electrically couple theelectrical via 644 with an electrical via 662, thereby electricallycoupling the two coils in series. This results in an in-series coil pairthat encircles the patient's torso. The in-series pair may be coupled toa recharging device (not shown in FIG. 16) through conductors 664 and666 that are carried in cable 670. A recharging device may be used togenerate a current in the in-series coil pair to induce magnetic fluxlines that are substantially parallel to the spine of a patient donningthe device. This magnetic field more optimally induces a current in asecondary recharge coil carried within an IMD of an angled device, suchas one that lies in a plane substantially perpendicular to the spine ofthe person donning belt 630.

In one embodiment, belt has an intermediate portion 676 of belt that isformed of a material that is expandable and contractible to allow a userto select the distance between the two coils. For instance, intermediateportion 676 may be formed of an accordion-like material having folds orpleats. This may be useful when recharging IMDs that are not locateddirectly at a person's waist. For instance, if the IMD is implantedhigher in a patient's abdominal cavity, the bottom of belt may bepositioned approximately at the patient's waist, whereas the top of thebelt may be extended upward by expanding intermediate portion 676towards the patient's pectoral region. This allows the coils to surroundan IMD that is implanted higher in the chest region. Alternatively, thebelt may simply be donned at a higher position around the patient'storso.

The embodiment shown in FIG. 16 is designed to fit a torso having apredetermined girth. Belt 630 may be made more versatile by providingmultiple sets of male contact members and/or multiple sets of femalecontact members along the length of conductors 636, 638, 640, 646, 648,and 650.

FIG. 16 illustrates an embodiment wherein the coils are electricallyarranged in series and encircle the patient's torso. The current in thecoils is generated using a single pair of conductors 664 and 666 thatmay be coupled to a single port of a recharging device. In analternative embodiment, the coils need not be in-series, but instead mayeach be coupled individually to the recharging device via a respectivecable. In this type of configuration, belt 630 may be modified toeliminate conductor 660, which arranges the coils in series. Instead,the recharging device will drive the two coils individually, as may beaccomplished using two ports. In one implementation, the rechargingdevice will drive the coils so that the current in each of the two coilshas the same amplitude, frequency, and phase.

FIG. 16 further illustrates that the turns of the coil need not beco-planar. For instance, conductors 646, 648, and 650 are connected toform a three-turn coil. The turns of the coil are “stacked” one on topof another rather than residing in a same plane as they would if theturns of the coils were concentric. Thus, the three-turn coil may besaid to be carried in multiple planes that are substantially parallel toone another and share a same major axis. This major axis issubstantially perpendicular to each of the multiple planes that carrythe coils, and this major axis further intersects the centers of theturns of the coil. In this embodiment, this major axis would beapproximately parallel to a spine of the patient that is donning belt630.

In accordance with the foregoing, conductors 636, 638, and 640 areconnected to provide a first coil that may be described as lying in afirst plane. That first plane is one of multiple substantially parallelplanes that carry the turns of the first coil, which are stacked one ontop of each other. Likewise, conductors 646, 648, and 650 areinterconnected to provide a second coil that lies in a second plane,wherein that second plane is one of multiple substantially parallelplanes that carry the turns of the coil. The second plane may bedescribed as being substantially parallel to the first plane. When belt630 is donned by a patient, an IMD that residing in an abdomen or torsoregion of the patient is situated between the first and second planes. Arecharging device coupled to each of the first and the second coilsgenerates a current in the first and the second coils thatelectromagnetically couples the first and the second coils to asecondary recharge coil to recharge a rechargeable power source of theIMD.

FIG. 17 is a cross-sectional exploded view of ends 632 and 634 of belt630 illustrating how these ends overlap when the belt is donned. Inparticular, this view illustrates how a conductor at end 632 of the belt630 is electrically coupled to a conductor at the other end 634 of beltwhen the belt is donned. In this particular example, conductor 638 atend 632 is shown being coupled to conductor 640 at end 634, althoughthis discussion applies equally to the other conductors of the belt.

As mentioned previously, conductor 640 is electrically coupled to anelectrical via 642. This via 642 extends through to the underside ofbelt 630 and electrically couples to, or is integral with, a respectivemale contact member 680 formed of electrically-conductive material.Similarly, conductor 638 at end 634 is electrically coupled to a femalefastening member 682 that is on the front side of belt 630. When belt630 is configured in a loop as to encircle a patient's torso in themanner shown in FIG. 16 so that end 632 overlaps with end 634, femalefastening member 682 aligns with male fastening member 680. The malefastening member 680 may be snapped into position to engage femalefastening member 682, thereby providing mechanical coupling of the twobelt ends, and also electrically coupling conductor 638 to conductor640. In an alternative embodiment, the female fastening member mayreside at end 632 and male fastening member may be located at end 634.

In FIG. 17, conductors 638 and 640 are each illustrated as being araised member that protrudes from the surface of belt 630. This need notbe the case. The conductors may be embedded within the fabric or othermaterial that forms belt 630. Moreover, the conductors may reside on theundersurface of the belt to make better contact with a patient's skin,particularly if the belt is worn under clothing. In this case, thecoupling of the conductors to the fastening members will be somewhatdifferent, since via 642 will no longer be needed, but a via may benecessary to couple conductor 638 to female fastening member.

FIG. 18 is another embodiment of a system that provides dual coils foran angled implant. In this embodiment, a first coil 700 is carried on,or embedded in, a support structure 702 on which the patient is seated.For instance, this support structure may be a cushion 702, a pillow, achair, a stool, or any other structure. This support structure may be aportable seat cushion that can be carried with the patient and thrown onany chair or stool during a recharge session. This first coil 700 may becoupled to a recharging unit via cable 704.

The system also includes a garment 710 such as a vest that may be donnedby sliding it over a patient's head and arms. The vest carries a coil712 (shown dashed), which in one embodiment has the same number ofturns, dimensions, and coil properties as coil 700. The coil 712 may becarried on, or in, a bell-like projection 714 that extends from thebottom of garment 710, as may result in optimal electromagnetic couplingin some situations. In another embodiment, coil 712 may be merelycarried around the lower edge of the vest that is substantially parallelto the patient's body rather than bowed away from the body. In eitherembodiment, the coil may be carried by the garment using stitching,adhesive, hooks, hook-and-loop strips, ties, or any other fasteningmechanism that may be used to affix coil 712 to garment 710.

The garment may include means to allow the coil height to be adjustableso that the coil is positioned optimally for the height of the implantwithin the patient. For instance, garment 710 may include a layer offolded or pleated material that is similar to portion 676 of belt 630(FIG. 16). In one embodiment, this allows coil 712 to be positioned sothat an IMD within patient 718 is approximately midway between coils 700and 712.

Coil 712 is coupled to a recharging device via cable 716. The rechargingdevice drives the two coils individually, generating current in bothcoils 700 and 712 so that magnetic flux lines are generated that areapproximately parallel to the patient's spine to optimally recharge anIMD that is angled within the patient's body. In one embodiment, thegenerated current is the same in both coils.

FIG. 18 illustrates that the turns of a coil may be oriented such thatsome turns are inside of the other turns, rather than being stacked ontop of each other, as shown in FIG. 16. For example, one or more turnsof coil 700 have a smaller circumference than, and are located within,one or more other turns of the coil 700. The various turns of coil 700may, but need not, be co-planar. Thus, coil 700 may not only have someturns that are “wrapped inside” the other turns of the coils, but coil700 may also have some turns that are “stacked” on other turns. Allturns of the coil are substantially concentric.

Likewise, in one embodiment, some turns of coil 712 may have a smallercircumference than other turns of the coil. The turns of the coils may,but need not, be co-planar to one another. For instance, because of theshape of bell-like projection 714, an inner turn of coil 712 that has asmaller circumference than another turn of coil 712 may reside in aplane that is farther from coil 700 than the plane that carries an outerturn of coil 712. That is, the turn with the smaller circumference is“above” the turn with the larger circumference. In a differentembodiment, the reverse may be true, and a turn of coil 712 with alarger circumference may reside in a plane that is farther from coil 700than another turn of the same coil with a smaller circumference. Thatis, the turn with the larger circumference is “above” the turn with asmaller circumference.

The foregoing illustrates that a coil of the current invention may be ofany number of turns. The turns may be stacked one on top of the other,and/or the turns may reside one inside the other. The turns may residesubstantially in a single plane, as may, but need not, be the case whenthe turns reside one inside the other, as depicted by coil 700. When theturns of a coil reside in multiple planes, these planes will besubstantially parallel to one another.

FIG. 19 is another embodiment of a garment 750 having two coils thatencircle, or wrap around, a portion of the patient's body. This garmentmay be any type of shirt, vest, jacket, sweater, or another type ofgarment to be donned by an upper portion of the patient's body. Coils754 and 752 (shown dashed) each encircle the patient's torso when thegarment is donned, and may be provided on the underside of the garmentto allow for better coupling with the patient. They are shown coupled torecharging device 756, which drives the coils individually. Anembodiment may be provided that has an intermediate conductor (similarto that shown in FIG. 16) that electrically couples the two coils inseries so that they may be driven by a single port of recharging device756. Resulting magnetic flux lines will couple to a secondary rechargecoil of IMD 758 (shown dashed) that is angled within the patient's body.

FIG. 19 further illustrates how the turns of the coils may be “stacked”one on top of another, as was the case in the embodiment of FIG. 16.Thus, the turns of coil 754 are not co-planar, but rather reside inmultiple planes that are substantially parallel to one another. A majoraxis of the coil lies substantially perpendicular to the multiple planesthat carry the coil. Likewise, turns of coil 752 are not co-planar, butrather reside in multiple planes that are substantially parallel to oneanother.

In accordance with the foregoing, first coil 754 may be described aslying in, or being carried by, a first plane, wherein that first planeis only one of multiple planes in which this first coil lies. Likewise,coil 752 may be said to lie in a second plane, which is one of multipleplanes in which coil 752 is carried, or lies. The second plane may bedescribed as being substantially parallel to the first plane. Whengarment 750 is donned by a patient, IMD 758 lying in an abdomen or torsoregion of the patient is situated between the first and second planes.In a more particular embodiment, a plane carrying a secondary coil ofIMD 758 may be substantially parallel to, and may lie between, the firstand second planes to result in optimal inductive coupling between thefirst and second external coils and the secondary coil.

Similar coils may be provided to recharge an angled implant located inother portions of the patient's body. For instance, coils 760 and 762(shown dashed) may be provided to recharge an angled IMD 764 (showndashed) located within a patient's arm.

FIG. 20A is a band 780 that carries two coils 782 and 784 (showndashed). This band may be sized to fit around a portion of the patient'sbody in which an IMD is implanted, such as an arm, a wrist, a leg, anankle, a head, a foot, a neck or any other body part. For instance, thisband may be positioned around a patient's head to recharge an IMDimplanted within the brain. The band may include an optional elasticportion 786 that is provided to retain the band in a selected positionaround the desired portion of the body. When in position, the IMD willlie between the two coils.

In a variation of FIG. 20A, headwear may be provided that carries twocoils. The coils are configured in a manner similar to that shown inFIG. 20A such that when the headwear is donned, the coils encircle thepatient's head. The headwear may be a cap, a hat, a headset thatsupports the coils so that they encircle the patient's head, or anyother type of mechanism worn on the head for supporting the coils inthis manner.

FIG. 20B is a garment 790 to be worn around the lower portion of apatient's torso according to the current invention. This garment may beshorts, pants, or any another garment of this nature. The garmentincludes coils 792 and 794 (shown dashed). When the garment is donned,these coils encircle a portion of the patient's leg for recharging arechargeable power source of an IMD that is positioned between the twocoils. In another adaptation, coils 796 and 798 (shown dashed) may beprovided for an IMD located within the torso.

FIG. 21 is a flow diagram of one exemplary method for using the currentinvention. First and second coils are provided that lie in first andsecond planes, respectively (800). The coils are external to a patient'sbody. These coils are positioned so that the IMD lies somewhere betweenthe first and second planes and so that the first and second planes aresubstantially parallel to each other (802). The IMD may lie anywherebetween the coils, although best recharge efficiency may be achievedwhen the IMD is positioned roughly half-way between the coils.

As discussed above, positioning step 802 may involve wrapping the coilsaround some portion of the patient's body, which may include the head,neck, arm, hand, wrist, chest, torso, leg, ankle, foot, or any otherportion. Alternatively, this may involve placing the coils on opposingsides of the patient's body, such as a front and back of a torso, on twosides of the torso, or on any other two opposing surfaces of thepatient's body.

The first and the second coils may optionally be positioned so that theyshare a same major axis (804). Additionally, the major axis may bealigned to intersect the IMD, and even to coincide with a major axis ofthe IMD, if desired (806). While this may result in a most efficientrecharge session, the coils need not be aligned as described in steps804 and 806 in an alternative embodiment.

In step 808, the first and second coils may then be coupled to arecharging device so that the coils are electrically arranged in-series(e.g., via a same port), or so that the coils will be drivenindividually (e.g., via different ports). A current is then generated inthe first and second coils to electromagnetically couple the first andthe second coils to a secondary coil of the IMD to recharge arechargeable power source of the IMD (810). This electromagneticcoupling is described in the foregoing embodiments as inductivecoupling. However, other forms of electromagnetic coupling are possiblewithin the scope of the current invention, such as RF coupling. In oneembodiment, the current generated in a first coil has the sameamplitude, frequency, and phase as that generated in the second coil.

It will be understood that the above-described embodiments are merelyexemplary and many other embodiments are possible within the scope ofthe current invention. The coils may be carried by any one or morestructures that are different from, or used in a different combinationas compared to, the exemplary structures described herein. For instance,one coil may be carried on a garment and the second coil carried on atorso strap. As another example, a coil may be incorporated directlyinto the fabric of a chair, or even a seat of a car so that rechargingmay occur when a patient is seated is his car. In this latter case, asecond structure such as a mechanism coupled to the car may suspend asecond coil around the patient while the patient is driving.

As described herein, any types of coils known in the art are possiblefor use with the current invention. For instance, pancake coils or anyother type of coils may be used. The coils may have any number of turns.Moreover, turns of the coils may be stacked one on top of another,and/or one or more turns may have a smaller circumference and resideinside or within one or more turns having a larger circumference. Turnsof a coil may reside in a more angled configuration as shown in regardsto coil 712 of FIG. 18, wherein a coil turn having a smallercircumference is not co-planer with a coil having a largercircumference. Thus, many types of coils and coil configurations arepossible within the scope of the current invention.

It should also be appreciated that while the foregoing embodiments aremost beneficially employed with an IMD that is implanted at a depth ofgreater than 3 cm and/or that has a secondary recharge coil that isangled within the body so that this coil is not parallel to adjacentsurfaces of the patient's body, the techniques described herein may beused in other scenarios as well. For instance, they may likewise beemployed for IMDs implanted closer to a cutaneous boundary and that havea secondary recharge coil that is substantially parallel to thiscutaneous boundary. To this end, it should be understood that the IMDmay be closer (and in some cases significantly so) to one coil ascompared to the other coil, and need not be equally spaced between thecoils. Thus, the description is to be considered illustrative only, withthe scope of the invention to be determined by the Claims that follow.

1. A system, comprising: first and second primary coils configured to bepositioned external to a patient; and a circuit configured to drive thefirst and second primary coils at a same time such that the first andthe second primary coils are electromagnetically coupled to one anotherand to a secondary coil configured to be implantable within a patient.2. The system of claim 1, wherein the secondary coil is positionedsubstantially between the first and second primary coils.
 3. The systemof claim 1, wherein the circuit is configured to generate a current inthe first primary coil having a same amplitude, phase, and frequency asa current generated in the second primary coil.
 4. The system of claim1, wherein the first and the second primary coils are electricallycoupled to one another in series.
 5. The system of claim 1, wherein thesystem is configured to drive the first and the second primary coilsindividually.
 6. The system of claim 1, wherein the first and secondprimary coils are substantially parallel to one another.
 7. The systemof claim 1, wherein the first and second primary coils are configured totransfer energy to the secondary coil by inductively coupling to thesecondary coil.
 8. The system of claim 1, wherein the first and secondprimary coils are configured to transfer energy to the secondary coil byRF coupling to the secondary coil.
 9. The system of claim 1, furthercomprising: the secondary coil; and at least one circuit configured tobe implantable within the patient and to be powered by energytransferred to the secondary coil by the first and the second primarycoils when the first and the second primary coils areelectromagnetically-coupled to the secondary coil.
 10. The system ofclaim 9, wherein the at least one circuit of the implantable medicaldevice is a therapy module to deliver therapy to a patient.
 11. Thesystem of claim 10, wherein the therapy module is configured to treatincontinence.
 12. The system of claim 1, further comprising: thesecondary coil; and a rechargeable power source configured to beimplantable within the patient and to be recharged by energy transferredto the secondary coil by the first and second primary coils when thefirst and the second primary coils are electromagnetically-coupled tothe secondary coil.
 13. A method, comprising: positioning first andsecond primary coils external to a patient; and driving the first andsecond primary coils at a same time such that the first and the secondprimary coils are electromagnetically coupled to one another and to asecondary coil that is implantable within a patient.
 14. The method ofclaim 13, wherein driving the first and second primary coils comprisesgenerating a current in the first primary coil having substantially asame amplitude, phase, and frequency as a current generated in thesecond primary coil.
 15. The method of claim 13, wherein driving thefirst and second primary coils comprises electrically coupling the firstand second primary coils to one another in series.
 16. The method ofclaim 13, wherein driving the first and second primary coils comprisesdriving the first and the second primary coils individually.
 17. Themethod of claim 13, wherein positioning the first and second primarycoils comprises positioning at least one of the first and second primarycoils so that a respective major axis of at least one of the first andsecond primary coils intersects an implantable medical device thatcarries the secondary coil.
 18. The method of claim 13, furthercomprising transferring energy from the first and second primary coilsto the secondary coil via inductive coupling.
 19. The method of claim13, further comprising transferring energy from the first and secondprimary coils to the secondary coil via RF coupling.
 20. The method ofclaim 13, further comprising powering at least one circuit of animplantable medical device via energy transferred from the first andsecond primary coils to the secondary coil.
 21. The method of claim 20,wherein the at least one circuit is a circuit to deliver therapy to thepatient.
 22. The method of claim 13, further comprising recharging arechargeable power source of an implantable medical device via energytransferred from the first and second primary coils to the secondarycoil.
 23. The method of claim 13, wherein positioning the second primarycoil comprises positioning the second primary coil so that the secondarycoil lies substantially between the first and second primary coils. 24.A system, comprising: first and second primary coil means fortransferring energy to a secondary coil implantable within the patient;and driving means for driving the first and second primary coils at asame time such that the first and the second primary coils areelectromagnetically coupled to one another and to the secondary coilmeans.